In spite of being color blind, I am a visual guy – I like to see things. Nothing beats a chart to identify problems in your data. I also spend lots of time manipulating data in FSI, the F# REPL, and while solutions like FSharpChart makes it possible to produce nice graphs fairly easily, I still find it introduces a bit of friction, and wondered how complicated it would be to use Excel as a charting engine.

Turns out, it’s not very complicated. The typical use case for generating charts in Excel is to first put data in a spreadsheet, and use the corresponding range as a source for a chart. However, it’s also perfectly possible to directly create a Chart object, and manipulate its SeriesCollection, adding and editing Series, which are arrays of XValues and Values.

As a starting point, I decided to focus on 2 problems:

plotting functions, in 2 and 3 dimensions,

producing scatterplots.

Both are rather painful to do in Excel itself – and scatterplots are the one chart I really care about when analyzing data, because it helps figuring out whether or not some variables are related.

What I wanted was a smooth experience from FSI – start typing code, and ship data to Excel, without having to worry about the joys of the Excel interop and its syntax. The video below shows what I ended up with, in action.

Note: watching me type is about as exciting as watching paint dry, so I sped up the video from its original 5 minutes down to 2 - otherwise there is no trick or editing.

I am still toying with the idea of using FSI from within Excel – wouldn’t it be nice if, instead of having to resort to VBA or C# via VSTO, I could leverage F#, with unfettered access to .NET and a nice scripting language, while having at my disposal things like the charting abilities of Excel?

Judging from the discussion on Twitter this morning, it seems I am not the only one to like the idea of F# in Excel:

I am still far from this perfect world, and wouldn’t mind some input from the F# community, because I am having a hard time figuring out where the sweet spot is. At that point, what I have is a pretty rudimentary WPF FSI editor, written in C#.

Note: yes, I should have written it in F#, shame on me! I am still more comfortable with the WPF/C# combo at the moment, but getting increasingly uncomfortable with XAML and the amount of magic string involved in data binding. Jon Harrop presented some very stimulating ideas on this topic at the last San Francisco F# user group, I intend to try the NoXAML route at a later point.

Anyways, you can find my rudimentary editor here on GitHub, with a crude WPF demo. Running it should produce something like this:

I quite liked how FsNotebook organized the code into blocks and separated the inputs and outputs, so I followed the same idea: you can add new sections at the top and evaluate each one separately, and see the result at the bottom. There is obviously plenty of work to do still, but at least this is a working prototype.

Note: the code is still pretty ugly, and totally not ready for prime time. Specifically, resources aren’t disposed properly at all – use at your own peril!

I have been obsessing about the following idea lately – what if I could run a FSI session from within Excel? The motivation behind this is double. First, one thing Excel is good at is creating and formatting charts. If I could use F# for data manipulation, and Excel for data visualization, I would be a happy camper. Then, I think F# via FSI could provide an interesting alternative for Excel automation. I’d much rather leverage existing .NET libraries to, say, grab data from the internet, than write some VBA to do that – and the ability to write live code in FSI would be less heavy handed that VSTO automation, and closer to what people typically do in Excel, that is, explore data. Having the ability to execute F# scripts would be, at least for me, very useful.

Seeing Tim Robinson’s awesome job with FsNotebook.net kicked me out of procrastination. Even though FsNotebook is still in early development, it provides a very nice user experience – on the web. If something that nice can be done on the web, it should be feasible on a local machine.

As an aside, Tim is looking for feedback and input on FsNotebook – go try it out, it’s really fun:

Anyways – this is the grand plan, now we need to start with baby steps. If I want to embed FSI in Excel (presumably via a VSTO add-in), I need a way to talk to FSI from .NET, so that I can create a Session and send arbitrary strings of code to be evaluated.

As usual, StackOverflow provided two good starting points (this answer, and this answer) – so I set out to look into the Process class, which I didn’t know much about, and attempted to spawn a FSI.EXE process, redirecting input and output. Turns out it’s not overly complicated – here are the 34 lines of code I ended up with so far (see it on GitHub):

This is a fairly straightforward class. The constructor expects the path to FSI.EXE, and sets up the process in the constructor (the do block) to run headless and redirect the stream of inputs and outputs. Start() simply starts the process, and begins reading asynchronously the output of FSI, AddLine(line) is used to add an arbitrary string of F# code, and Evaluate() sends all lines currently buffered to FSI for evaluation – and flushes the buffer. The 2 events OutputReceived and ErrorReceived are provided for the client to listen to the FSI results.

I am putting together a demo VSTO add-in for my talk at the Excel Developer Conference. I wanted to play with charts a bit, and given that I am working off a .NET model, I figured it would be interesting to produce charts directly from the data, bypassing the step of putting data in a worksheet altogether.

In order to do that, we simply need to create a Chart in a workbook, add a Series to the SeriesCollection of the chart, and directly set the Series Values and XValues as an array, along these lines:

Using LINQ, we Select from the list the values we are interested in, and pass them into an array, ready for consumption into a chart, and boom! We are done.

If what you need to do is explore data and produce charts to figure out potentially interesting relationships, this type of approach isn’t very useful. On the other hand, if your problem is to produce on a regular basis the same set of charts, using data coming from an external data source, this is a very interesting option!

Earlier this month, on Simon Murphy’s blog, the project to organize a UK Excel Developer conference 2012 in London quicklytookshape. As of now, the planned date is in the January 24 to 26 range, with a pretty cool agenda, covering most of the recent developments Excel developers should know about. I am looking forward to it!

I’ll be talking for about an hour on VSTO (Visual Studio Tools for Office). VSTO can be both awesome and painful: I plan on demoing building an Excel add-in from the ground up, illustrating some of the benefits and drawbacks/pitfalls of that approach, so that you know when it’s the right time to go that route.

If there are any topics or questions you are specifically interested in, please let me know in the comments – I’ll be happy to take requests.

As an aside, I usually talk at .NET developers events, where I need to convince the audience that developing for Excel (or Office) isn’t a terrible idea. This will be my first time with an Excel developers audience, and I expect the opposite challenge, namely why bother with C#/VB.NET and Visual Studio when VBA is free and works just fine?